The health of the American public and the affordability of U.S. healthcare are both threatened by inefficiency in the U.S. healthcare system. A broad array of public and private sector payment and delivery system reforms is underway, the aim of which is to improve care, improve health and slow spending growth. The success of these reforms, however, requires reliable approaches to measuring health quality and costs while accounting for potential differences in patient risk. And while consensus has emerged that current approaches to risk adjustment and performance monitoring have serious limitations, the impending broadscale adoption of electronic health records is expected to enable the routine collection of extensive individual biomarker and patient-reported measures of risk, symptoms and functional status. The current proposal is intended to advance the science of health risk, health outcome and health system performance measurement while helping to address pressing policy needs. The project will draw on important data assembled in Core C: detailed individual risk and health status data from the Health and Retirement Survey (HRS), newly collected patient-level data from three diverse health systems, and comprehensive Medicare claims data. Under the first aim, which focuses on risk adjustment, we will develop two new risk-adjusters: (a) one based on the detailed biometric and patient-reported data collected through the HRS, and (b) a second based on integrating ZIP code and county level measures of health status, mortality and disease incidence. These will be compared to the claims-based measures currently used by Medicare for program payment, with the aim of informing both long-term and interim approaches to improving risk adjustment. Under the second aim, we will use the patient risk and biometric data collected in routine clinical practice to explore potential limitations to using these data for risk adjustment and performance measurement, including assessing the degree to which non-response bias is likely to be problematic, how their routine use in primary care practices is perceived by clinicians, and whether their use contributes to improved care for Medicare patients.